Basic sediment and water (BS&W) constitutes a fraction of one percent of the crude oil transferred into and out of a conventional pipe-line system. Various methods have been developed for measuring the BS&W content of crude oil. For example, samples of the curde can be taken and analyzed for BS&W content. Also, it is possible to use capacitor-type measuring instruments to measure the BS&W content of the crude as it flows through a meter and eliminate the need to take samples. The latter approach is favored, since it permits automatic operation without requiring the attention of outside personnel to obtain representative samples and conduct analysis of the crude. Also, the signal from the BS&W monitor can be used to compensate the flow meter or other measuring instruments to correct for the BS&W content.
The BS&W monitors of the capacitance type, which detect water by means of change in dielectric constant of an oil stream flowing through a conduit, suffer from a number of disadvantages. While the capacitance monitor may be extremely accurate, it is often adversely affected by certain uncommonly existing conditions. For example, the monitor must measure a homogenious mixture in order to achieve a permissible degree of accuracy. Laminar flow in which the oil and liquid tend to separate into different phases is not conducive to efficient monitor operation. Also, slug-type flow in which successive slugs of water and oil flow through the line adversely effects the monitor. A more serious problem arises when the type of crude oil is changed, since this requires a change in the calibrating standard of the BS&W monitor. Since all capacitance-type monitoring equipment measures the dielectric strength of the material disposed between the plates of the measuring cell, any change in the dielectric constant of the crude requires a correponding change in the monitor which cause measurement interruption and gives rise to further chances of error. Of course, even a small error of measuring can result in a substantial financial loss due to the extremely large quantities of oil moving through the pipeline.